The present invention relates to depth gauge grinders for saw chains and more particularly to such a grinder that will grind all of the depth gauges of a saw chain to the same predetermined height.
The cutter links of chipper and chisel saw chains have depth gauges for regulating the depth of cutting by the cutter elements of such links. The depth gauges are ordinarily established at a predetermined height somewhat lower than the leading edges of the cutter elements. During sharpening of the cutter elements, the top cutting edge of each cutter element is lowered slightly because of the downward and rearward slope of the cutter element's top plate. Thus, to reestablish the proper vertical relationship between the top edge of the cutter element and the depth gauge, the top of each depth gauge should also be reground when the saw chain is sharpened.
It is desirable that the depth gauges of different cutter links all be of the same height for smooth cutting action. Thus, it is necessary to be able to lower the depth gauge grinder to precisely the same grinding position during the grinding of the depth gauges of successive cutter links. It is also desirable to be able to precisely and repeatably position successive depth gauges in a grinding position beneath the grinding wheel to grind the tops of the gauges to substantially identical, usually flat, profiles. Finally, it is necessary to avoid inadvertently grinding the cutter elements while repositioning the chain beneath the grinding wheel for grinding successive depth gauges. Prior saw chain grinders meet some but not all of these requirements.
U.S. Pat. No. 2,811,874 to P. Rethoret and my own U.S. Pat. No. 3,779,103 disclose adjustable pawls for holding a saw chain cutter link with its depth gauge in a grinding position beneath the grinding wheel. However, neither of these patents disclose means for preventing the grinding wheel from contacting other cutter elements of the cutter links during repositioning of the saw chain.
My U.S. Pat. No. 3,717,051 discloses a depth gauge grinder in which the grinding wheel is automatically lifted over the cutting element when the saw chain is being repositioned on the saw chain holder to grind the depth gauges of successive cutter links. Such grinder employs a pivotable lever member positioned adjacent the grinding wheel so as to be engaged and lifted by each cutter link passing beneath such member. Lifting of the lever member actuates a connected linkage to lift the grinding wheel away from the saw chain and thus allow the cutter element following the depth gauge to pass beneath the grinding wheel. Damage to the cutter element is thereby avoided. However, reliance on a cutter link itself to actuate the linkage which lifts the grinding wheel away from the cutter link is, at least in some instances, undesirable because of the inherent lateral instability of the saw chain on its holder. Such instability can introduce uncertainties and inconsistencies in the operation of the lifting mechanism, causing it to malfunction by failing to lift the grinder a sufficient distance to clear a cutter link, resulting in inadvertent grinding of and damage to the cutter elements.
Accordingly, there remains a need for an accurate depth gauge grinder which will reliably and preferably automatically prevent inadvertent grinding of cutter elements during chain repositioning to grind successive depth gauges.